Device for detecting quality alterations in bulk goods transported on moving belt conveyors

ABSTRACT

A device for detecting quality alterations in bulk goods transported on moving belt conveyors comprising a pulsed, monochromatic light source (1), frequency multipliers (2) and dichroic mirrors (3) or prisms to simultaneously generate several light beams having different wavelengths and irradiate several spots (6) of the flow of bulk goods on the belt conveyor (7). In addition, a detector unit is provided for observing the irradiated spots (6) in the flow of bulk goods for measuring excited photoluminescence, reflected light and temperatures, as well as for carrying out signal analysis with time resolution. The triggering of the device is adapted to the running speed of the belt conveyor (7) and allows the same area of the moving flow of the bulk goods to be irradiated several times in the spots (6) with beams having different wavelengths. The signal analysis includes detecting signal intensity and the fading behaviour of the signals in defined spectral ranges. The device does not affect operation of the belt conveyor but makes possible the control of subsequent devices.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for detecting qualityalterations in bulk goods on moving belt conveyors.

2. Description of the Prior Art

Through a publication by SYMONDS, D. F., 1991, "On-Line Ash AnalysersImprove US Efficiency", MINTECH '91, pages 163 ff, Sterling PublicationsInternational Limited, London a device for determination of the ashcontent of bulk coal on belt conveyors is known, which by means of gammaray absorption and backscatter measures the density of the material and,thus, indirectly the ash content of the coal. Devices of this kind havebeen marketed for more than 25 years by various manufacturers, as e.g.by the company "Laboratorien Prof. Dr. Berthold GmbH und Co.", Wildbad,Germany.

Analytically, these devices are hampered by measuring the density of amixture of different matter only and, thus, can indicate indirectly onlythe amount of a certain component in simple mixtures.

The Finnish company "Outokumpu Electronics Oy" also markets devices ofsaid kind, where the type "Beltcon 100" operates with gamma rays, whilethe type "Beltcon 200" is based on X-rays. The technical paper "MiningJournal", London, UK covered these devices in its issue of May 1991.

In general all above mentioned devices, which operate with gamma rays orX-ray fluorescence, have the disadvantage, that the radioactive sourcesused pose a health risk during maintenance and transport and that aftertheir useful life have to be disposed of.

Devices for the determination of quality parameters of bulk goods onbelt conveyors, which are based on the utilization of light of the UV toinfrared range, sofar are not marketed in a commercial way.

From literature methods and devices are known, which use light beams ofa defined wavelength to observe various matter, as e.g. country rock andcoal in a mine, or individual components of goods on belt conveyors, ase.g. diamonds in ore from diamantiferous orebodies, or even tomatoes,and to provide information for directing, splitting or blending ofmaterial.

The German patent DD 293 748 A5 of the Martin-Luther-Universitat,Halle-Wittenberg of the year 1990 describes a "Verfahren und Vorrichtungzum Sortieren von Tomaten nach ihrem Reifegrad" (Method and Device forSorting Tomatoes According to Their Ripeness). The use of a light sourcewith a defined wavelength for the irradiation of tomatoes is disclosed,which depending on their respective degree of ripeness displayphotoluminescence of different intensity.

The published patent application DE 38 18 588 A1 of "BergwerksverbandGmbH", Essen, Germany of the year 1988 desribes a "Verfahren undAnordnung zur Unterscheidung unterschiedlicher Materialien" (Method andDevice for Differentiation Between Different Matter). Here the use ofone or various systems for irradiation and observation at definedexcitation wavelengths and defined wavelength bands for observation todifferentiate for example between coal and country rock is mentioned.

The two patent applications GB 2 219 079 A and GB 2 219 082 A by thecompany "Gersan Establishment" of Liechtenstein of the year 1989disclose devices for concentrating diamantiferous ore, where the devicesare specified having one light source operating at one definedwavelength and two or more receiver systems.

Already in the year 1980 the Canadian company "Scintrex Limited" ofConcord, Ontario in the British patent GB 2 089 029 A gave a detaileddescription of a "Method and Apparatus for the Remote Detection ofCertain Minerals of Uranium, Zinc, Lead and Other Metals". Here also onelight source with one emitted wavelength or, for a multi-channel system,various light sources with one defined wavelength each for theexcitation of photoluminescence are mentioned.

The Australian company CSIRO, "Commonwealth Scientific and IndustrialResearch Organisation", in 1989 applied for the U.S. Pat. No. 4,959,549"Determination of Properties of Coal". The surface of coal on a beltconveyor is irradiated with UV light and the intensity of thephotoluminescence is measured. A comparison of the measured signals withreference data leads to the determination of relevant properties of thecoal. In this application also one light source with one definedwavelength is to be used.

It is known, that the intensity of photoluminescence depends on thewavelength of the excitation. These relationships are described inBROICHER, H. F., 1987, "Naturwissenschaftliche, technische undwirtschaftliche Aspekte bei der Entwicklung und Nutzung einesPhotolumineszenz-Sensors fur die Rohstoffprospektion" (Scientific,Technical and Economic Aspects for Designing and Operating aPhotoluminescence Sensor for Prospecting for Raw Materials), Verlag yonDietrich Reimer in Berlin, Germany.

Therefore, for the precise determination of individual minerals or thealteration of the composition of a mixture of minerals it is desirableto operate at various wavelengths when exciting photoluminescence.Furthermore it is known, that the absorption and reflection at distinctwavelengths as well as the thermal inertia of minerals can be utilizedfor their respective determination.

According to the state-of-the-art, for each specific wavelength onelight source is required, the light source preferentially being a laser.If the material shall be irradiated at various distinct wavelengths,then various light sources are required. Such a device will become verydemanding regarding costs, space and energy consumption.

SUMMARY OF THE INVENTION

It is the objective of the present invention to provide a device of saidkind that is .capable of observing the bulk goods on a belt conveyor andof detecting quality alterations of bulk goods by means of excitation ofphotoluminescence, by irradiation at a wavelength with specificreflectance and by thermal irradiation.

It is the basic idea of the present invention in contrast to prior artdevices,

not to equip the device with a laser as the source of light, whichdirectly irradiates the material with monochromatic light, so that formulti-channel systems various lasers have to be installed,

but to produce with only one laser as the source of light varioussimultaneous light beams at different wavelengths by means of frequencymultipliers and, thus, to measure and analyze

the photoluminescence typical for the bulk goods or for one component ofthe bulk goods after excitation at a suitable wavelength,

the photoluminescence after excitation with a wavelength different fromthe first wavelength land less effective and/or

the reflectance of this irradiation and

the thermal inertia or absorption of infrared light.

Bulk goods transported on belt conveyors generally are minerals as forexample limestone, phosphate ore, iron ore, uranium ore, potash, rocksalt, ores of the non-ferrous metals, ores of the rare earths, beachsands with heavy minerals, hard coal, lignite and oil shales.

All these materials and also mixtures of these as well as country rockmined exhibit a photoluminescence signal, either inherent or caused bycontamination, when properly excited. It is known that some minerals'photoluminescence is short lived, that is, the decay time offluorescenmce is less than 200 nanoseconds (nsec). To measure andanalyse such a short signal the excitation or at least the extinction ofthe excitation has to happen in a very short time of a few nanosecondsonly. A pulsed laser is a suitable source of light.

An especially suited laser for the present objective of material testingis a Nd:YAG laser emitting at a wavelength of 1,064 nm.

According to the present invention, a frequency multiplication beam willproduce distinct wavelengths of 1,064, 532 and 266 nm. The UV lightcomponent at 266 nm is especially suited for excitation ofphotoluminescence in most minerals. The green light component at 532 nmalso can excite photoluminescence in some minerals and will be evaluatedin reflectance measurements. The infrared component facilitates thermaland reflectance measurements.

Selection of the specific wavelength for each channel is done by meansof dichroic mirrors, which might also expand or focus the light beams,if already manufactured as concave or convex components. The use of aprism for the separation of the different light beam components also ispossible.

If the material on the belt conveyor is irradiated and observed invarious equidistant spots of identical size, triggering of the systemdepending on the speed of the belt conveyor is realized in such a way,that always the same areas of the material are irradiated by the variouslight beams and, consecutively, are observed. Thus it is achieved, thatin continuous operation each area is irradiated by each distinct lightbeam and that the signals produced are received and evaluated.

BRIEF DESCRIPTION OF THE DRAWING

By means of the embodiment shown in the drawing the invention shallfurther be described.

The drawing shows schematically the preferred embodiment of the devicein side elevation.

In the drawing a belt conveyor (7) is shown with the bulk goods on it.For irradiation of areas on the surface of the bulk goods with light atdifferent wavelengths in the spots (6) there are arranged above the beltconveyor (7) a laser (1) and attached to it a frequency multiplier (2),mirrors (4) for deflection and dichroic mirrors (3) as well as lenses(5) for beam expansion. Furthermore, according to the number of spots(6) there are installed various detector systems with optical componentsto view the spots (6), filters (9) for selecting wavelength bands forevaluation and photodetectors (10). The electronic means for triggeringthe system and for analysis of the electric signals is not shown.

We claim:
 1. A device for detecting variations in the quality of bulkgoods during transport on a moving belt conveyor comprising:a) a pulsedmonochromatic light source for producing a pulsed monochromatic lightbeam; b) a frequency multiplying means for frequency multiplying saidlight beam to produce a frequency multiplied light beam having aplurality of wavelengths; c) a selecting and deflecting means forselecting a plurality of light beams, each having a defined wavelength,from said frequency multiplied light beam, and for deflecting each ofsaid selected light beams toward the moving belt conveyor carrying thebulk goods to be detected such that the belt conveyor is simultaneouslyirradiated at a plurality of defined regions arranged in the directionof conveyor movement; d) a detector means operatively associated witheach of said defined regions for detecting electromagnetic energyemitted therefrom following irradiation, each of said detector meansincluding a reflector, a filter and a photodetector; and e) a triggeringmeans for controlling the pulse of said light source, said pulse being afunction of belt conveyor speed whereby a designated portion of the bulkmaterial is sequentially irradiated by each of said directed light beamsas it travels along the belt conveyor.
 2. Device according to claim 1,wherein said pulsed light source (1) is a laser.
 3. Device according toclaim 2, wherein said laser is emitting monochromatic light at awavelength in the range of 230 to 1,200 nanometers (nm), said laser is aNd:YAG laser, which emits at a wavelength of 1,064 nm.
 4. Deviceaccording to claim 1, wherein said frequency multiplying means is asingle frequency multiplier that doubles or quadruples the frequency ofthe monochromatic light or various frequency multipliers to producemultiplication of frequencies of the monochromatic light and, thus,light beams having multiple distinct wavelengths.
 5. Device according toclaim 1, wherein said frequency multiplying means is a single frequencymultiplier that quadruples the frequency of the monochromatic light,thus generating from an incoming light source wavelength of 1,064 nm abeam with 532 nm and 266 nm, respectively.
 6. A device as in claim 1 andwherein:a) said selecting and deflecting means includes a lens forexpanding each of said deflected light beams.
 7. A device as in claim 1and wherein:a) said selecting and deflecting means includes a dichroicmirror.
 8. A device as in claim 1 and further comprising:a) a beamexpander means for expanding each of said deflected light beams.
 9. Adevice as in claim 1 and wherein:a) said selecting and deflecting meansincludes a prism.
 10. A device as in claim 1 and wherein:a) saidfrequency multiplied light beam having wavelengths selected from thegroup consisting of ultraviolet light, visible light and infrared light.